PHIVOLCS reported that during the previous 11 weeks, since the Alert Level for Taal was raised to 2 (on a scale of 0-5) on 9 April, the number of earthquakes recorded daily gradually declined, hydrothermal activity abated, carbon dioxide gas emissions decreased, ground temperature and total magnetic field measurements in the main crater showed no significant changes, and deformation data showed no signs of increasing pressure. On 5 July the Alert Level was lowered from 2 to 1.

As previously reported (BGVN 32:01), during the last four months of 2006 Taal displayed restlessness. This report discusses Taal seismicity, deformation, and hydrothermal behavior (steaming, and temperature changes in lake water at Main Crater) that occurred intermittently during 2008, 2010, and 2011.

Taal (also known as Talisay) is a lake-filled, 15 x 20 km caldera located on SW Luzon Island 65 km S of Manila (figure 9). The lake engulfs a large island with several thousand residents, Volcano Island, the place where all historical eruptions have vented (figures 10 and 11). Restlessness described herein was not confined to the area beneath the island.

Figure 9. Index map of the Philippines showing Manila (the Capital) and several major volcanoes including Taal. Courtesy of Lyn Topinka (US Geological Survey).

Figure 10. A map showing Taal caldera and surroundings. Notice that the caldera lies at the intersection of major faults and the topographic margin extends well beyond the caldera lake's margin. Courtesy of NASA Earth Observing System (EOS) Volcanology and their slide set compiled by Peter Mouginis-Mark (University of Hawaii).

Figure 11. Photo of the Taal caldera lake and Volcano Island taken from the N in November 1999. Courtesy of NASA Earth Observing System (EOS) Volcanology and their slide set compiled by Peter Mouginis-Mark (University of Hawaii).

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) announced in August 2008 that seismic unrest continued. On 28 August 2008, ten volcanic earthquakes occurred, two of which were felt and heard as rumbling sounds by residents in the Pira-Piraso village on Volcano Island. The earthquakes were located NE of the island near the Daang Kastila area (below Taal caldera's N rim) at estimated depths of 0.6-0.8 km. Surface observations indicated no change in the main crater lake area. The Alert Level remained at 1 (scale is 0-5, with 0 referring to No Alert).

On 8 June 2010, PHIVOLCS raised the Alert Level for Taal to 2 because of changes in several monitored parameters that began in late April. Since 26 April, the number and magnitude of volcanic earthquakes had increased. Most signals were high-frequency earthquakes, but at least one, on 2 June, was low-frequency. Steam emissions from the N and NE sides of Main Crater occasionally intensified. Deformation data showed slight inflation since 2004; measurements taken at the SE side of Taal on 7 June showed further inflation by 3 mm.

In addition to increased seismicity, the temperature of the Main Crater Lake increased from 32°C on 11 May to 34°C on 24 May. According to PHIVOLCS, the ratios of Mg:Cl and SO4:Cl, as well as total dissolved solids in the lake, all increased. Temperature measurements of the main crater lake did not increase further, remaining between 33-34°C.

PHIVOLCS proposed that the high frequency earthquakes could be the result of active rock fracturing associated with magma intrusion beneath the volcano, and that the fractures could serve as passageways through which hot gases from the intruding magma could escape into the lake.

According to news reports (Xinhua, Philippine Daily Inquirer), the more than 5,000 residents living near Taal were advised to evacuate their homes voluntarily. On 10 June, the Philippine Coast Guard sent five teams of divers and rescue swimmers with rubber boats and medical teams to its forward command post to help evacuate, if necessary, these residents. A news report (Philippine Daily Inquirer), however, indicated that most residents refused to leave without an official order.

The number of earthquakes recorded daily gradually declined to background levels beginning the second week of July 2010. Hydrothermal activity in the N and NE sides of the main crater and Daang Kastila also decreased. Precise leveling measurements conducted during 13-21 July along the NE, SE, and SW flanks detected minimal inflation. On 2 August, PHIVOLCS lowered the Alert Level to 1.

According to PHIVOLCS, seismic activity increased during the first week of September 2010. From 1-27 September 2010, a total of 274 volcanic earthquakes, or an average of 10 events/day, was recorded. However, given that field surveys conducted at the Main Crater and at the 1965-1977 "New Eruption" site (SW edge of Main Crater) indicated no anomalous thermal or surface activity.

PHIVOLCS reported that a December 2010 deformation survey showed slight inflation compared to a September 2010 survey. Field observations on 10 and 18 January revealed no significant changes. Weak steaming from a thermal area inside the main crater was noted and the lake temperature, acidity, and color were normal. During 15-16 January 2011, ten volcanic earthquakes were detected, two of which were felt by residents of Pira-Piraso, on the N side of the island. On 17 January three volcanic earthquakes were detected and on 18 January only one was reported. Between 18-30 January, up to seven daily volcanic earthquakes were detected by the seismic network.

Field observations during 23-25 January 2011 revealed an increase in the number of steaming vents inside the main crater and a drop in the lake level there. The lake water temperature and pH values remained normal. Visual observations on 27 January showed weak steaming at a thermal area in the crater.

Weekly Reports - Index

PHIVOLCS reported that during the previous 11 weeks, since the Alert Level for Taal was raised to 2 (on a scale of 0-5) on 9 April, the number of earthquakes recorded daily gradually declined, hydrothermal activity abated, carbon dioxide gas emissions decreased, ground temperature and total magnetic field measurements in the main crater showed no significant changes, and deformation data showed no signs of increasing pressure. On 5 July the Alert Level was lowered from 2 to 1.

PHIVOLCS reported that field measurements conducted on 24 May at the E sector inside Taal's Main Crater Lake showed that the water temperature slightly increased from 32.5 to 32.8 degrees Celsius, the pH value became more slightly acidic decreasing from 2.83 to 2.67, and the water level increased by 4 cm. During 25-29 May, between 6 and 10 daily volcanic earthquakes were detected by the seismic network. Some of the earthquakes were felt by nearby residents on the SE part of the island. During 29-30 May, 115 earthquakes were recorded. Twelve of these events were felt at Intensity I-IV by residents of Pira-piraso, Alas-as, and Calauit located in the NE, SW, and SE sectors of Volcano Island, respectively. During 30-31 May there were 31 earthquakes noted. The Alert Level remained at 2 (on a scale of 0-5).

During 12-19 April, PHIVOLCS reported that between 6 and 19 daily volcanic earthquakes at Taal were detected by the seismic network. Some of the earthquakes were felt by nearby residents on the SE part of the island. The Alert Level remained at 2 (on a scale of 0-5).

During 12-19 April, PHIVOLCS reported that between 6 and 21 daily volcanic earthquakes at Taal were detected by the seismic network. Some of the earthquakes were felt by nearby residents. Results of a ground deformation survey conducted around Volcano Island during 5-11 April showed that the edifice was slightly inflated compared to a survey from early February. The Alert Level remained at 2 (on a scale of 0-5). According to news articles, the number of people that had evacuated from around Taal rose to 1,375.

PHIVOLCS reported that field observations of Taal conducted at the E sector inside the main crater lake on 5 April 2011 showed that steaming at the thermal area was weak. The water level had receded 3 mm and the water temperature slightly increased from 30 to 30.5 degrees Celsius. Since the previous measurement on 29 March, the pH value increased indicating that the water had become slightly less acidic. Gas measurements conducted last January, February, and March yielded carbon dioxide emission values (in tonnes per day) of 2,250, 1,875, and 4,670, respectively.

On 9 April PHIVOLCS noted that after 31 March the number of earthquakes gradually rose and the depths become more shallow (1-4 km). Steaming at the N and NE sides of the main crater occasionally intensified and was occasionally accompanied by hissing sounds. The Alert Level was raised to 2 (on a scale of 0-5) because of increased seismicity and carbon dioxide emissions. PHIVOLCS warned tourists and residents to avoid Volcano Island. According to news articles, about 100 families had volunteered to evacuate; about 7,000 people remained.

During 25-27 and 29-30 January, PHIVOLCS reported that up to six volcanic earthquakes at Taal were detected daily by the seismic network. Field observations during 23-25 January revealed an increase in the number of steaming vents inside Main Crater and a drop in the lake level. The lake water temperature and pH values were normal. Visual observations on 27 January showed that steaming at a thermal area in the crater was weak. The Alert Level remained at 1 (on a scale of 0-5).

PHIVOLCS reported that field observations of Taal on 18 January revealed steam rising from the thermal area inside the Main Crater. Temperature and acidity of the lake were at normal levels, and the color had not changed. During 18-25 January, up to seven daily volcanic earthquakes were detected by the seismic network. The Alert Level remained at 1 (on a scale of 0-5).

PHIVOLCS reported that a deformation survey of Taal conducted in December 2010 showed slight inflation as compared to a survey conducted in September 2010. Field observations on 10 January revealed no significant changes. Weak steaming from a thermal area inside the main crater was noted and the lake temperature and color were normal. During 15-16 January 10 volcanic earthquakes were detected; two earthquakes were felt by residents in barangay (neighborhood) Pira-piraso, on the N side of the island. On 17 January three volcanic earthquakes were detected and on 18 January only one was reported. The Alert Level remained at 1 (on a scale of 0-5).

PHIVOLCS reported observations during the previous eight weeks after the Alert Level for Taal was raised to 2 (scale is 0-5, with 0 referring to No Alert status) on 8 June. Temperature measurements of the main crater lake did not increase further since 8 June, remaining between 330 and 340 degrees Celsius. The number of earthquakes recorded daily gradually declined to background levels beginning the second week of July. Hydrothermal activity in the N and NE sides of the main crater and Daang Kastila also decreased. Precise leveling measurements conducted during 13-21 July along the NE, SE, and SW flanks detected minimal inflation. On 2 August, PHIVOLCS lowered the Alert Level to 1.

On 8 June, PHIVOLCS raised the Alert Level for Taal to 2 (scale is 0-5, 0 referring to No Alert status) due to changes in several monitored parameters, starting in late April. Since 26 April the number of earthquakes per day continued to increase, as well as the magnitude. Low-frequency volcanic earthquakes were detected on 2 June, and during the previous day high-frequency earthquakes were noted. In addition to increased seismicity, the temperature of the Main Crater Lake increased from 32 degrees Celsius on 11 May to 34 degrees Celsius on 24 May. Steaming from the N and NE sides of Main Crater occasionally intensified. Deformation data had shown slight inflation since 2004; measurements taken at the SE side of Taal on 7 June showed further inflation by 3 mm.

PHIVOLCS reported ongoing seismic unrest at Taal on 28 August. Ten earthquakes occurred; two at Intensity II were felt by residents in the Pira-Piraso village and were accompanied by rumbling sounds. The earthquakes were located NE of the island near the Daang Kastila area at estimated depths of 0.6-0.8 km. Surface observations indicated no change in the main crater lake area. PHIVOLCS warned that the main crater was off-limits to the general public. The Alert Level remained at 1 (scale is 0-5, 0 referring to No Alert status).

According to news articles, geysers of muddy water 3-5 m high occurred in the NNE portion of Taal's main crater during 17-21 November. On 24 November, a new episode of 50-cm-high geyser activity and increased seismicity prompted PHIVOLCS to raise the Alert Level from 1 to 2.

PHIVOLCS reported ongoing seismic unrest at Taal on 26 September. During 25-26 September, 29 volcanic earthquakes occurred with five felt Modified Mercalli intensities of II to III. Epicenters were dispersed NE, N, and NW. Approximately five seismic events in a 24-hour period is typical during quiet periods.

PHIVOLCS raised the Alert Level at Taal from 0 to 1 (on a scale of 0-5) on 29 October due to an increase in seismicity at the volcano. The seismic network at Taal began to record significant volcanic earthquakes on 23 September. In general, through 29 October the number of earthquakes increased, with a maximum of 13 earthquakes recorded on 15 October. Initial epicenter locations were in the vicinity of Main Crater and to the NNW near Binintiang Malaki and to the SSE near Calauit. No significant changes in thermal and steam emissions were observed. PHIVOLCS recommended appropriate vigilance by the public when visiting the island and noted that Main Crater was off-limits to visitors because of the potential for sudden steam explosions and high concentrations of noxious gases.

Information is preliminary and subject to change. All times are local (unless otherwise noted)

September 1968 (CSLP 21-68)

Increased steaming from cone area

Card 0041 (09 September 1968) Increased steaming from cone area

The following information was reported in the "Daily Mirror" on 31 August 1968. " . . . the Commission on Volcanology revealed today that Taal volcano's abnormal condition still persists. Arturo Alcaraz, chief volcanologist, said steaming activity has increased considerably on the base and slopes of the cone formed in the last eruption. He also said that the steaming is very noticeable today from several areas of the 1968 lava flow in Kaygabok."

October 1968 (CSLP 47-68)

The following report was received on 7 October 1968. The volcanology commission reported last night that Taal volcano had entered another active period that could culminate in another eruption. Seven volcanic quakes and tremors were recorded in a 24-hour period. COMVOL observers on Volcano Island also reported that there was intensified surface thermal activity, confirming that the volcano's condition was abnormal. COMVOL headquarters in Quezon City recommended that precautionary measure be taken particularly the complete evacuation of Volcano Island. Volcanologist Nazario Vasquez reported that instruments have picked up seven volcanic quakes and tremors from Taal's depths, clearly indicating its restlessness. Vasquez said surface steaming, rise of temperature readings in all ground probe holes, and other intensified activity in the main crater lake may all culminate in another eruption.

The following report was received from the American Embassy in Manila on 8 October 1968. Signs Taal volcano resurgence plainly inferred by existing field and instrumental data. Surface activity at 1968 cone has gained momentum. Despite absence rains for last two or three days which might have brought about condensation steaming and emission sulfuric vapors very strong this morning. In addition, fresh slide scars attest volcano's restlessness as seismicity of island continued. Three more volcanic quakes picked up commissions seismograph; one 1758 on 7 October; another 1915 on 7 October, and third at 1106 on 8 October.

The following report was received from the American Embassy in Manila on 11 October 1968. Seismic activity again picked up rapidly. For the 24-hour period beginning 1530 on 9 October through 1530 on 10 October. A total of five volcanic quakes were recorded by the COMVOL seismograph on Volcano Island, at 1853 and 2454 on 9 October; and at 0233, 0235, and 1008 on 10 October. Field observations conducted early this morning (10 October) at the 1968 eruption cone disclosed fresh evidence of rock slide, indicating recent movement within the volcano. Chloride and sulfuric sublimate have spread almost throughout NW outer slope of cone.

Card 0122 (11 October 1968) High level of seismic activity returns

The following report was received from the Commission on Volcanology on 6 October 1968. Taal volcano shook more strongly the past 24 hours. The volcano is back to its high-level seismic activity, convulsing five times through Sunday morning. A quake recorded at 0933 on 6 October was big enough to have an amplitude of 17 mm. The usual amplitude of earthquakes at Taal volcano since it became restless again was 4-5 mm.

The following report was received from the American Embassy in Manila on 14 October 1968. As of 13 October the surface activity and seismicity were both weak for the last 48 hours. As of 14 October at 1530 the four-day seismic lull was broken by eight volcanic microseisms of appreciable magnitude. Crater lake temperature was decreasing, but steam emission was intensifying, especially at the SW shoreline of the lake.

The following report was received from the American Embassy in Manila on 15 October 1968. Taal status as of 15 October 1530 hours. High level of seismic disturbance. Intensification of surface thermal activity.

Card 0145-0146 (17 October 1968) Crater lake temperature increases 2.5° in two days

The following news report was received on 17 October 1968. "The temperature of Taal volcano's main crater lake suddenly went up today (9 October) from 36.5 to 39°C, a sharp rise of 2.5°C in two days. The next heat reading, according to volcanologists here, exceeds that recorded in the same lake when Taal volcano erupted in 1966 (36.5°C) and early this year (34.2°C). This is, however, slightly lower than the heat reading of 39.6°C registered before Taal erupted in 1966.

"Assistant chief volcanologist Gregorio Andal expressed fears that pressure and heat buildup from below may increase some more before the volcano erupts for the second time this year. He said, however, that a bigger blast can be reasonably expected to occur because more volcanic energy will be needed this time to throw out tons of earth and lava blocking the exit. 'Conditions similar to the 1965 eruption now exist in Kaigabok' Andal said, pointing out that smaller crater lakes in the same area in 1966 and 1967 have all been covered by earth and lava.

"Volcanologist Pedro Almoradie Jr. and junior volcanologist Conrado Andal Jr. reported the new heat increase in the 1911 main crater lake this morning after making an on-the-spot observation. Almoradie said aside from the heat rise, emission of steam in the southwestern shores of the main crater lake was observed to be intermittent occurring every five to ten minutes. He also said all the steam vents facing Binintian Malaki started emitting more steam and vapor this morning.

"Meanwhile, volcanic tremors from below quieted down for the past 24 hours despite the rising temperature in the main crater lake. The COMVOL said the seismic lull may only be temporary because all other conditions on the island are abnormal. Strict enforcement of precautionary measures under phase on of Operations Taal is now being observed."

December 1968 (CSLP 47-68)

"COMVOL Bulletin 2300 hours 12 December. Anticipated second activity Taal about to commence. Small but continuing local vibrations recorded by Volcano Island seismograph. If persistent could bring expected eruptive activity."

"Taal's surging volcanic pressure, which last Thursday night was manifested as continuous ground vibrations, seems to have been blocked. The continuous tremors have been replaced by spasmodic volcanic earthquakes often associated with crustal deformation. In the last 24-hour period, eleven (11) more shocks of this type were recorded in the COMVOL's seismographs. These developments suggest that the volcano's pent-up energy is trying to punch through and initiate an eruptive activity. As present indications point to a persistent pressure from below, the condition of Taal remains critical and a surface out-break of this pressure is perhaps just a matter of time."

October 1969 (CSLP 133-69)

Eruption of ash and incandescent fragments on 29 October

Card 0810 (29 October 1969) Eruption of ash and incandescent fragments on 29 October

The following is from the Commission on Volcanology via the American Embassy in Manila. Taal eruptive activity commenced at 0615 on 29 October. Point of activity on upper outer southern slope of 1968 cone characterized by weak ejection ash and small fragmental materials at approximately 90-minute intervals. COMVOL visual observation during afternoon showed appreciable increase in amount ash and fragmental red hot volcanic materials and considerable enlargement in diameter of active vent. Increase in trace amplitude of harmonic tremors and explosion earthquake also noted. Night and early morning observations 30 October showed ejection of ash and fragments to heights of 600-700 feet at about 90-minute intervals. Continuing recording of harmonic tremors and observable pulsating vent flows seems to indicate vibration of lava to surface. Eruption is now violent though protracted.

The following is from the Commission on Volcanology via Father Hennessey. Taal Volcano erupted at 0615 on 29 October. Ashes and fragments were ejected up to 900 feet at 90-minute intervals shooting up from a roaring vent about 5 m in diameter. During early hours of 30 October observations show sections of ash and incandescent fragments to 600-700 feet at varying but closer intervals compared to previous observations. Proportion of incandescent material noted increased since yesterday. Continuous recording of harmonic tremors and observable pulsating dense flow seems to indicate that lava vibrating to the surface.

November 1969 (CSLP 133-69)

"Lava clots began appearing on 30 October 1969, with incandescent materials being thrown out by the erupting Taal volcano. The bits of molten rock from the surging column of lava are falling on the upper southeastern slope of the 1968 cone.

"The chief volcanologist, Mr. Alcaraz, said that the coming eruption of Taal will not be of steam and ash but will be magmatic or cool lava. The volcano's pulsating magma has been surging with mounting intensity and frequency. The erupting vent has been enlarged and now measures almost 100 m in diameter. Taal's ejecta is being blown upward to a height of 1,500 feet. The lava column may surface in a few days, overflow, and fill the southeastern base of the 1968 cone. A protracted magma eruption might cover the thick lava deposits of the 1968 eruption in Kaygabok."

Card 0820 (10 November 1969) New cone rapidly growing on the SE slope of the 1968 crater

"Taal volcano is rapidly building a new cone southwest of Volcano Island on the southeastern slope of the 600-foot-high crater created by last year's eruption in Kaygabok. The conelet is now about 200 feet high. The cone's lava front advanced further into the 1966 collapsed lake on the Northeast. The lava front is more than 1 km long and is moving at the rate of 1 m per minute. The stream may eventually flow into Lake Taal. The lava, measured by a optical barometer, was found to be 1,160°C. Volcanologists said that harmonic tremors are getting stronger every day. The chief volcanologist, Mr. Alcaraz, said that this eruption is the second in recorded history where the volcano emitted more lava than ashes. The ejecta reached a height of 1,000 feet above the crater, which was widened to 20 m in diameter."

The following is from the American Embassy in Manila. "Taal's current uninterrupted eruption entered 4th week this morning with activity still characterized by sustained and copious ejection of ash and incandescent fragmental materials at active vent of imposing terminal cone of 1968 eruption (former adventive cone but now too large for such designation). Ejecta has been primarily vertical but occasionally radial. Yesterday's ejections accompanied by large detonation sounds and blue-tinted gas. Subterminal flows at base in terminal cone continue molten rock discharge at intensified rate to adjacent area. Front advanced into lake southwest of island."

The following is from J.J. Hennessey. "COMVOL reports at 0800 local time on 18 November. Evenings activity was more intense than that observed this morning. Ejecta was primarily incandescent bombs and blocks shot up vertically but at time ejected with a radial trajectory. Near 1730 a black column of ash started to burst out from a smaller vent on the inner western slope of the 1969 crater. This lasted for about one half hour. Lava extrusion continued without let up, the subterminal flow breaking out into four or five cascades over a rift formed by crushed lava near the northern base of the old 1968 cone. Discharge to Lake Taal is likewise continuous."

December 1969 (CSLP 133-69)

"The old eastern vent of the terminal cone belches noxious blue fumes continuously. From both the eastern and western vents a faint glow and a profuse steaming are observed. The Kaygabok and Alas-as lava fronts, fed by molten rocks flowing through tunnels underneath the crusted lava surface, continue to fan out very slowly lakewards. The easternmost lobe at Kaygabok has moved no less than 2 m in two days.

"Voluminous emission of steam characterized the eruption surface manifestation as Taal's eruption entered its 27th day. Intense steam emissions were concentrated in the western vent of the terminal cone and the former crater of the 1968 cone, now covered by new pyroclastic materials deposited by the current eruption.

"A new vent of the northwestern upper slope of the 1969 cone has been formed. Sustained ejection of steam, ash, and small amounts of larger incandescent volcanic materials from the new active vent have enlarged the crater and reduced the height of the terminal cone to a few meters. The spiraling brownish-grey ash clouds soar 4,000 feet, then accumulate at a higher altitude before drifting southwest. Comparatively stronger ejections are punctuated by weak and muffled roaring sounds."

Card 0834 (09 December 1969) Signs that activity may shift to a new submarine vent in Lake Taal

The possibility of a new eruption occurring beneath Lake Taal or near Mt. Binintiang Munti, southwest of volcano island, has increased. The shifting of the site of the volcano's activity and signs of an approaching eruption forced COMVOL to enlarge the danger area to include villages on the lake's western shore. The COMVOL said that there were indications that the volcano was nearing a "critical phase" of its activity. Observed were: 1) A noticeable upliftment of the ground in the vicinity of Binintiang Munti on volcano island; the ground rose by one foot. 2) Bubbling of lake waters on the side parallel to the southwest ridge. 3) Maximum trace of the amplitude of the harmonic tremors emanating from the volcano showed a continuing upward trend, although no surface outflow of lava has been observed. 4) Collapse of the lava front in the area of what was once Kay-gabok village, which was leveled at the height of the Taal eruption. 5) Strong mustard odor from the bubbling point discerned by volcanologists and people living near the island. At the moment, the volcano's activity was reportedly limited to the ejection of incandescent materials and ash to about 1,500 feet.

December 1970 (CSLP 113-70)

"The Philippine Volcanology Commission issued the following bulletin on 29 December at 2300 GMT. COMVOL progressive evaluation of the condition of volcano Taal indicates that it has remained critically serious as visual and instrumental observations continue. COMVOL will issue the next bulletin after today's visual observation of the volcano's geologically active southwestern rift. Manila time 30 December gives COMVOL report for 29 December. An intensity 2 quake rocked Taal volcano at 0829 today and steam came out in the Kaygabok eruption site along a NE-SW rift leading to the main crater. The team issued the following bulletin. 1) Profuse steaming was noted on the NE upper slopes of the 1969 eruption cone and from a point a little to the NE. 2) A fresh landslide was noted. 3) The temperature of the main crater lake dropped by 1.5°C from yesterday's temperature. 4) The NE-SW rift passing through the main crater is active."

Precursors trigger evacuation before explosive eruptions in early September

COMVOL scientists monitoring Taal during late August noted the following signs of increased activity: profuse steaming from the junction of the SW portion of the 1966-70 eruption cone and the western rim of the pre-1965 lagoon (figure 1); visible ground heating at some points above the pre-1965 lagoon; and a rise in the temperature of some ground probes in the area to 95°C. As a result of these observations, the evacuation of several thousand persons from Taal Island ("Volcano Island" on figures 1 and 2) and some lakeshore towns was recommended on 31 August.

Figure 1. Index map showing the area around Taal, after Moxham (1967). Land area is shaded.

Figure 2. Map of Taal Island and vicinity, October 1965, after Moxham (1967). The 1965 explosion crater extends SW from I; the 1966 explosion crater formed immediately to the NW.

2 September: Steaming increased at the 1966-70 eruption site and at the main crater. The area of steaming had expanded considerably, particularly to the SW. A fissure widened from 5 to 20 cm and lengthened from 50 to 100 m. Seismic activity was low.

3 September: An eruption of steam and ash began at about 0430 from Mt. Tabaro vent, a few meters SW of the site of 1966-70 activity. Eruptions occurred at about 4-minute intervals, producing clouds 1,500-3,000 m high. Harmonic tremor accompanied the activity. Evacuation had been completed at 0400.

4 September: Eruptive activity ceased at 0500. Renewed steam and ash emission occurred between 0900 and 0920 and again at 1300; the latter included some large fragments and produced a cloud 300-400 m high. Harmonic tremor was recorded during eruptions. Brownish ash blanketed the S half of the island to an unknown depth.

5 September: Individual eruptive bursts contained a greater proportion of ash and large fragments than those of previous days. No incandescent material or rumbling was observed. During the morning, eruption periods were longer than the repose periods separating them; by late afternoon, eruptions lasted about 3 minutes, followed by about 5 minutes of repose. Eruptions were nearly vertical with a slight southward component; the resulting clouds reached more than 2,000 m in the morning, but were limited to 300 m by strong SW winds in the afternoon. Late-afternoon rain caused steaming to intensify. Continuous harmonic tremor of 4 mm amplitude was recorded. The new vent was enlarged by coalescence with the adjacent cone.

6 September: Harmonic tremor amplitudes began to increase at 0330 to 3-10 mm. Emission of black, grayish-black, or reddish-brown ash-laden eruption clouds was continuous, accompanied by faint rumbling and occasional brief lightning flashes just above the vent. The eruption clouds, which contained some large rock fragments, averaged 200-300 m, reaching a maximum of 2,200 m in the early morning. Activity had slackened by afternoon, when maximum eruption cloud height was slightly more than 500 m, and the diameter was about 50 m. Lower ejection velocity and light wind caused much of the erupted material to collapse and form base surges at the foot of the 1966 cone. Rock fragments up to 30 cm in diameter produced dust clouds on the 1966 cone by impact and downslope rolling. By 1700, activity was still continuous, but the eruption cloud had diminished to 30 m across and less than 500 m high. Maximum harmonic tremor amplitude had declined.

7 September: Steam and ash eruptions continued, generating a 3,000-m cloud and base surges over the SW flank. Harmonic tremor was continuous and had a maximum amplitude of 5 mm. A new fissure opened, measuring 100 m x 20 cm.

8 September: After a midmorning period of quiescence, a new vent opened a few meters SW of the active vent of the past several days. Ash and larger fragments were ejected to 250 m height. Maximum harmonic tremor amplitude increased to 8 mm.

9 September: The strongest explosion of the eruption produced base surges that moved over the 1965 and 1966 craters. Harmonic tremor amplitudes rose from 5 to 9 mm shortly before the explosion, and reached a maximum of 12 mm during the explosion. By late afternoon, eruptive force had declined, but ash emission was still continuous and voluminous. Strong west winds carried the ash across Lake Taal to its E shore.

10 September: At 2331, incandescent gases and some incandescent fragments were noted for the first time, accompanied by a continuous hollow sound. Steam and ash emission continued.

13 September: Voluminous quantities of steam and ash were emitted, causing ashfalls at towns up to 10 km E of the vent. Harmonic tremor was continuous. Intermittent incandescence was reported during the previous week.

14 September: Strong steam and ash eruptions continued until evening, when activity slackened.

15 September: Activity increased around 0700. Just before noon, a strong explosion ejected rock fragments 150 m above the vent and produced an 1,800-m ash. Ash fell on towns surrounding Lake Taal, up to 16 km E and N of the vent. One mm of ash fell in a 20-minute period and a strong stench of sulfur was noted at the volcano station, 4 km from the vent.

17 September: Ash fell continuously on towns east and north of Lake Taal, frequently mixing with rain to fall as mud. Heavy ashfall and sulfur fumes forced the evacuation of Taal Island, except for a skeleton staff remaining at the volcano station. Many work animals had died and many others were ill, probably because of sulfur-contaminated food and water. Harmonic tremor gradually increased in amplitude.

19 September: Diminished activity allowed an inspection on the vent area. The new crater formed on the first day of the eruption was steaming weakly. Most activity was from a 100-m-diameter vent within the 1965-70 cone, on which scattered impact craters a few centimeters to 0.7 m across were present up to 500 m from the vent. Harmonic tremor amplitude had declined. Ash emission weakened further in the evening, with occasional brief pauses. Ash clouds took 2-3 minutes to rise 700 m.

4 October: The eruption resumed after a "short lull." Ash clouds rose more than 2,100 m, accompanied by lightning, thunderstorms, and harmonic tremor.

5 October: Ash emission, in black to brownish clouds, increased. By afternoon, heavy ashfall, which forced cars to use their headlights, had deposited 2.5 cm of ash in one town near Lake Taal.

7 October: Continuous heavy ashfall forced the evacuation of five towns up to 16 km E and N of the vent. The eruption was accompanied by hollow sounds from within the crater and by harmonic tremor. Profuse emission of white steam was occurring from the source of the 1968 lava flow. A new step fault was noted near the summit of the vent.

8 October: Ash-laden steam clouds were ejected continuously to a height of 500-600 m, depositing ash around Lake Taal. Activity had migrated back to the elongate main vent. Harmonic tremor amplitude began to increase at 0330.

10 October: A reconnaissance at 1200 noted ejection of coarser fragments, accompanied by hollow reverberations, lightning, and thunder. Ash fell SW of the vent (most ash had previously fallen to the N and E). Ash eruption ended at 1650.

By 30 October, Taal's eruption had declined to weak steaming, and harmonic tremor had ended. Harmonic tremor resumed at 1925 on 30 October and steam eruptions began at about 2130. During the early morning of 31 October, cauliflower-shaped steam clouds reaching 100 m height were observed, containing only minimal amounts of ash. This activity continued through the day, the clouds gradually decreasing in height and volume. No further activity had been reported by 16 November.

A weak phreatic eruption from the NE portion of the 1976 crater began at 1515 on 3 October, and had ended by 1400 the next day. Brownish to grayish basaltic ash clouds initially rose 300 m, and reached a maximum height of 500 m after a few hours. Activity then gradually declined to strong steaming. The eruption was accompanied by harmonic tremor. Residents of Taal Island were evacuated, and had not returned by late October because of the possibility of renewed activity.

Taal ejected voluminous ash-laden steam clouds at 1200 on 9 November. The clouds, similar to those of 3 October, rose about 250 m before being blown toward the mainland by a moderately strong NE wind. Ground probe temperatures have increased, and harmonic tremor continued at about the same amplitude. Initial evacuation procedures remained in effect.

"The renewed activity of Taal on 9 November resulted in the formation of a circular conelet protruding a few meters from the floor of the elongated 1976 crater. Voluminous ash-laden clouds rose to a height of 500 m with a roaring sound audible on the lakeshore. Bluish fumes were emitted from the NE inner wall of the 1976 crater. Eruptive activity ended by the early morning of 12 November, but volcanic tremor of varying amplitude continued. Tremor with a maximum double amplitude was recorded at 2210 on 24 November and at 0504 on 25 November. The initial evacuation procedure remained in effect in late January."

"Recorded earthquakes began increasing 30 October. A maximum of 19 events/day was recorded on 31 October; 5 of the events were felt by residents of Agoncillo, 10.7 km SW of the crater on the W shore of Taal Lake (figure 3). The events were recorded but not felt on the volcano island, the site of historic eruptions in the Taal Caldera. Some residents of Agoncillo also reported rumbling sounds accompanying the earthquakes. Isolated reports of sulfurous stench were unconfirmed. Many residents of Agoncillo and nearby villages described the quakes as having prominent vertical movements, similar to those prior to the 1965 eruption, prompting a few families to immediately evacuate to adjacent villages. These areas were among those devastated during the 1965 phreatic explosion.

Figure 3. Map of crater lake and vicinity, after Land Use of Taal Volcano and Environs, PHIVOLCS, 1:50,000.

"Events on 6 November had epicenters on Manalao Point on the W shore of Taal Lake and across the lake from the 1965-77 eruption site (Mt. Tabaro; figure 3). The earthquakes had depths of 6.4 km and suggested ground fracturing beneath the caldera.

"Thermal conditions and steam emissions of the main crater lake and the 1965-77 eruption site remained within normal levels. However, the water-tube tiltmeter on the island indicated a slight inflation-deflation episode of the main crater 20 April-28 October, with the pre-inflation position now being occupied. Likewise, thermal areas near the epicenter have remained unchanged. Lake-level monitoring stations around Taal Lake, some installed only last July, indicate some warping along the lakeshore, a condition that cannot yet be related to volcanic activity.

"PHIVOLCS had installed additional seismic and ground deformation stations to monitor the events. Local authorities were informed and were prepared for any contingencies."

Seismic activity ... has abated and few local events have been recorded since 14 November. Thermal and steaming conditions remained unchanged from normal levels. Lake level monitoring showed some subsidence (about 10 cm) of the SW shores of Taal Lake, which face the 1965-77 eruption site on the volcano island. Residents who fled during the crisis have returned to their homes. PHIVOLCS established 3 EDM lines, 1 dry tilt network, and one precise leveling line on the island's SW sector near the 1965-77 eruption site. Volcanologists had also re-occupied old seismic stations on the SE part of the volcano island.

During a two-week period in mid-August, several small, high-frequency events with average maximum double amplitudes of 2 mm were detected at the Pira-Piraso seismograph station. From 16-22 August, 11 high-frequency events were recorded. Slight inflation was detected by the water tube tiltmeter at the station. Weak steaming continued at the 1965 eruption site. Ground-probe hole temperatures were within normal limits and the lake level remained unchanged.

Since July, seismicity at Taal has increased from background level to a maximum of 126 volcanic earthquakes/week, with at least three events recorded daily. Epicenters clustered around the main crater and about 2 km NE (near Pinagulbuan), migrating from 9 to 5 km depth, 18 August-2 October. Precise leveling and dry tilt surveys suggest inflation of the main crater and the 1965 eruption site, while a water tube tiltmeter has measured inflation of the main crater area since May.

Increased shallow seismicity and felt earthquakes; more than 1,000 evacuated

Seismologists and area residents noticed a significant increase in seismicity beginning on 12 March (figure 4). High-frequency earthquakes were recorded each day (to 64 on 25 March), of which several/day were felt (intensities to IV). Seismicity was centered under the E side of Volcano Island, at depths of 2-5 km.

Figure 4. Daily number of recorded earthquakes at Taal, 10 March-13 May 1991. Courtesy of PHIVOLCS.

Monitoring of the volcano's main crater lake (1.0 x 1.4 km) revealed that the acidity of the lake water has fluctuated considerably, between pH 2.3 and 3.8. Possible slight increases in water temperature (stable at 30°C in mid-April), a change in water color (from light yellowish-green to dark green), and more vigorous bubbling were also noted.

On 1 April, President Aquino ordered the evacuation of the roughly 4,000 people who live on Volcano Island, and more than 1,000 residents (mostly women and children) had left by the following day. Seismicity remained at elevated levels, and the island was partially evacuated as of mid-April.

High seismicity continued as of early May, with the daily number of earthquakes varying from 15 to 30 (figure 4). Felt earthquakes reached intensity IV. Acidity and chloride content of the volcano's crater lake continued to fluctuate, ranging from 2.4-2.8 and 9,630-11,720 ppm, respectively. Lake temperature increased slightly from 30° to 31°C, and lake level rose by 4 cm.

On 26 April, strong bubbling and increased steaming were observed in the N sector of the crater and at the base of the wall. Geysering, to 1.2 m height, was also noted near the NNE shore of the lake, where water temperatures of 99°C were measured.

Deformation measurements on Taal Volcano Island have found no inflation or swelling of the volcanic edifice.

Volcano Island has been partly evacuated since 23 March, but a small number of residents have remained, particularly near the PHIVOLCS station at the N end of the island.

Abnormally high levels of seismicity continued as of mid-August. Up to 5 small high-frequency earthquakes were recorded daily 9-12 August. No earthquakes were felt during this time. The main crater lake temperature remained at 31°C. Close monitoring of the volcano continued.

A sudden increase in local seismicity began early 14 February, reaching a peak of 385 high-frequency earthquakes recorded between 1200 on 14 February and 0600 on 15 February. Many were felt in 6 towns near the shores of Lake Taal, which fills the 15 x 22 km caldera. The active cone forms an island near the center of Lake Taal. According to press reports, volcanologists observed that water temperature in the island's crater lake (1.0 x 1.4 km) increased by several degrees, and that a bulge and several fissures (up to 400 m long) had formed on the volcano's N flank. A Notice to Airmen was issued at 1445 on 14 February, advising all aircraft to exercise caution and avoid flying over the area. PHIVOLCS elevated the volcano's status to Alert Level 3 on 15 February and authorities began to evacuate island residents. By the following day, >2,600 of the island's 6,000 residents had reportedly been evacuated. Seismicity quickly decreased on 15 February, and only 14 earthquakes were recorded during a 13-hour period on 16 February. Geologists suggested that the activity represented a magma intrusion episode that appeared to have stopped.

A similar episode of increased seismicity occurred in March-April 1991, with as many as 64 earthquakes (25 March) recorded under the E side of the volcano (16:3). Several thousand people were evacuated from the island. Seismicity decreased in May 1991, and no more than five earthquakes were recorded daily in early August . No inflation was observed.

After a brief episode of increased seismicity, deformation, and increased crater lake temperatures on 14-15 February, activity returned to more normal levels. Fieldwork by Univ of Savoie personnel indicated that temperatures of the main crater lake were gradually declining, and that seismicity was near background levels. All measurable deformation seemed to have occurred on 14 February. The Alert Level 3 status, announced on 15 February, was lowered to Level 2, and then to Level 1 in early March. Most residents of Taal island have returned home.

Beginning in late February 1994, Taal stratovolcano underwent increases in seismicity, deformation, temperature, and other signs of growing instability. The stratovolcano sits in the center of a 15 x 22 km caldera occupied by Taal lake. Taal stratovolcano, which is sometimes also referred to as either Volcano Island or Taal Island, has a central, 6-km-diameter crater lake termed the main crater lake (figures 5 and 6).

Figure 5. Map showing the key geologic and geographic features near Pinatubo and Taal.

Starting on 21 February seismic activity increased from the previous background level of 0-2 events/week to an average of 2-3 events/day. After 22 February, the seismic station located on the N shore of the main crater lake (station MRCZ) detected swarms of small high-frequency events, swarms that went undetected elsewhere, presumably because they had shallow epicenters located close to the station. Seismicity continued to grow; during the 24-hour intervals beginning at 0600 on 13 and 14 March there were 396 and 406 events, respectively. Many events took place at shallow depths (typically shallower than 3 km), beneath the central-to-SW portion of the caldera. Harmonic tremor was also reported, interpreted as due to magma intruding below the stratovolcano's central crater.

Deformation and precise leveling surveys conducted 10-22 February indicated slight inflation of the SW portion of Volcano Island. In mid-March an uplift of 14 cm was measured on the E side of the island; on 13 March both the N and SE sides inflated on the order of 10-20 cm. Around the same time researchers found two newly formed open cracks or fissures. They were approximately 70 m apart on the SE corner of Volcano Island, trending N55°W and N88°W, and were traced as discontinuous segments approaching the basal slopes of the main crater. The fissures had opened 8-10 mm, consistent with inflation of the edifice. Newhall and Dzurisin (1988) referred to extensive NE-trending ground cracks outside the caldera associated with the 1911 eruption.

Temperature measured near the bottom of the main crater lake rose abruptly on 13 February, from 30°C to 50°C, and remained high for about 12 hours before dropping back to 30°C. Eight days later a smaller 4°C rise in bottom-water temperature took place. Sometime during this interval the temperature of surface waters of the main crater lake also rose by 3°C. Temperature increases of 1-3°C began on 14 February at most of the ground probe holes in the Mount Tabaro area, on the SW side of Volcano Island (Ruelo, 1983).

On 12 March, data from acoustic sensors located about 25 m above the bottom of the main crater lake showed a significant increase in bubbling activity, which declined slightly the next day. The increased bubbling suggests significantly higher pressure beneath the stratovolcano, consistent with the postulated shallow magma chamber.

In response to growing instability PHIVOLCS elevated their alert status to Alert Level 3 on 11 March, suggesting that eruptive activity could occur within a period of weeks. In concert with the newly elevated alert level, the Manila Flight Information office issued a volcanic ash advisory in a NOTAM (Notice To Airmen, a notice to the aviation and meteorological communities) to avoid flying over the volcano. PHIVOLCS maintained Alert Level 3 as of the last available report on 15 March. They also mentioned "...partial evacuation of Volcano Island as per the recommendation of the Batangas Provincial Disaster Coordinating Council." The evacuations were a common theme in a series of reports by Reuters News Service on the situation at Taal. The reports were unclear, however, on both the number of people evacuated from Volcano Island, and the circumstances of their departure; one report told of hundreds who fled, the other told of thousands who were ordered to flee.

Several of these news reports also stated that some villagers from the island were unwilling to leave their homes. One report said "Farmers staying on the island have rented out horses to tourists from Manila so they can ride to the crater lake to photograph steam rising from rocks around the rim." The same report also said "Many sightseers have flocked to Tagaytay [on the N topographic Margin of the caldera, ~9 km N of Volcano Island], which offers a dramatic view overlooking the volcano." The Philippine president, Fidel Ramos, reportedly visited the volcano and said villagers who had refused to leave their homes would have time to flee if it erupted. These reports highlight the difficulty of establishing firm estimates on both the movement and behavior of people in a volcanic crisis.

Taal's most recent unrest took place in 1991-92 and involved elevated seismicity, deformation, and crater lake temperatures that lasted from several days to months. These conditions did not lead to eruptions. In many other cases, 34 since 1572, Taal did discharge, and in six cases these eruptions led to fatalities. In 1965 Taal ejected an estimated 9 x 107 m3 of material. The eruption had a Volcanic Explosivity Index (VEI) of 4 and produced a base surge that sandblasted objects up to 8 km away. The volcano monitoring system at Taal has been improved since the 1992 crisis. Improvements include telemetry-linked sensors for seismic, temperature, radon gas, and lake geochemistry. A Japanese refraction seismic experiment recently attempted to delineate a shallow (1-2 km deep) magma chamber beneath Volcano Island that was detected in a similar experiment in 1993.

The Taal seismic monitoring network began to record significant volcanic earthquakes on 23 September 2004. In general, the numbers of these events occurring through 29 October increased, with a maximum 13 earthquakes on 15 October. Some of these earthquakes were instrumentally recorded with relatively large amplitudes although none were felt by residents on Volcano Island. Initial earthquake locations showed epicenters dispersed in the vicinity of Main Crater, to the NNW near Binintiang Malaki, and to the SSE near Calauit. Surface observations, however, did not indicate any significant change in the thermal and steam emission characteristics of the Main Crater lake area. The increased seismicity is an indication of a low-level episode of unrest, although at this time there is no clear indication of an impending eruption. A series of volcanic earthquakes was recorded on 9 January 2005. Two of these earthquakes, only one minute apart, were felt in Pira-piraso.

PHIVOLCS raised the hazard status on 29 October from Alert Level 0 to Alert Level 1, meaning that there was a slight increase in seismic activity but no eruption is imminent. PHIVOLCS recommend as off-limits the Main Crater area because sudden steam explosions may occur or high concentrations of noxious gases may accumulate. Several fissures traversing the Daang Kastila Trail are also potentially hazardous as possible sites of future steam emission. PHIVOLCS is conducting several enhancements of the monitoring system at Taal with deployment of more seismometers and ground-deformation surveillance equipment. The entire Volcano Island is a Permanent Danger Zone and permanent settlement is strictly prohibited.

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) notified the public on 26 September 2006 of ongoing seismic unrest at Taal. The Main Crater Seismic Station recorded 29 volcanic earthquakes during the 24-hour period from 0600 hours on 25 September. Five of these earthquakes, at 0233, 0234, 0242, 0247, and 0249 hours on 26 September, were felt at Modified Mercalli Intensities II to III by residents on Volcano Island. The earthquakes were accompanied by rumbling sounds. Initial locations showed epicenters generally dispersed in the vicinity of Daang Kastila (NE), Tibag (N), Tablas (NE), Mataas na Gulod (NE), and Panikihan (NW). This seismic activity was notably higher than the usual levels, generally only five or less events detected in 24 hours.

Surface thermal observations, however, did not indicate significant change in the thermal and steam emission manifestations of the Main Crater lake area. The increase in seismicity at Taal reflects a low-level episode of unrest. However, there is still no indication of an impending eruption. Possible precursors, such as increased steam emission, increased temperatures of steam vents at the Main Crater lake waters and adjacent areas are being monitored continuously. The ongoing seismic unrest could intensify in the coming days or weeks so that PHIVOLCS recommends appropriate vigilance by the public when visiting the island.

On 26 September 2006, the Philippine Institute of Volcanology and Seismology (PHILVOLCS) announced ongoing seismic unrest at Taal (a low lying caldera ~ 45 km S of Manila). The Main Crater Seismic Station recorded 29 volcanic earthquakes during the 24 hours after 0600 on 25 September 2006. Five (5) of these occurred at 0233, 0234, 0242, 0247, and 0249 and were felt at Intensities II to III by residents on Volcano Island (figure 7 and 8). These earthquakes were accompanied by rumbling sounds. Initial computations showed epicenters generally dispersed toward northerly locations in the vicinity of Daang Kastila (NE), Tibag (N), Tablas (NE), Mataas na Gulod (NE), and Panikihan (NW).

Figure 7. A map of Taal volcano indicating the location of components of the monitoring network (seismic stations, telemetry repeater stations, reflector, and various kinds of survey and measuring points). Volcano island (the large island in the N-central part of the caldera lake) is the site of all historical eruptions. Contour interval is 100 m. Courtesy of PHIVOLCS.

Figure 8. Photograph taken from the top of the N topographic margin of Taal, looking S across Lake Taal and Volcano Island, 28 May 2001. The topographic high on the far side of the lake is Mt. Macolod. Copyrighted photograph by Franck Landais (provided by Panoramio.com).

This seismic activity was notably higher than usual, which during quiet periods is generally only five or less events detected in 24 hours. Surface thermal observations, however, did not indicate significant change in the thermal and steam emission manifestations in the Main Crater Lake area. The increase in seismicity reflected a low-level episode of unrest. However, there is still no indication of an impending eruption.

Taal manifested a sustained moderate level of seismic activity since 18 November 2006, characterized by occasional large amplitude volcanic earthquakes. During one 24-hour period, 10 volcanic earthquakes were detected. Ground deformation surveys conducted during 28 November-6 December 2006 revealed the edifice inflated 14.0 mm, suggesting possible magma intrusion. The Main Crater lake water became more acidic since 12 September 2006, and the newly formed mud geyser, which is now merged with the Crater Lake due to increase in water level, continues to be very active. The increasing acidity and hydrothermal activity are probably caused by the injection of hot gases and fluids coming from below the crater floor.

According to PHIVOLCS in its Taal Volcano Advisory of 14 December 2006, the above observations indicated a significant increase in activity although no eruption is imminent. Alert Level 1 continued, making the Main Crater off-limits to the public because of the chance of sudden steam explosions and high toxic gas concentrations.

As previously reported (BGVN 32:01), during the last four months of 2006 Taal displayed restlessness. This report discusses Taal seismicity, deformation, and hydrothermal behavior (steaming, and temperature changes in lake water at Main Crater) that occurred intermittently during 2008, 2010, and 2011.

Taal (also known as Talisay) is a lake-filled, 15 x 20 km caldera located on SW Luzon Island 65 km S of Manila (figure 9). The lake engulfs a large island with several thousand residents, Volcano Island, the place where all historical eruptions have vented (figures 10 and 11). Restlessness described herein was not confined to the area beneath the island.

Figure 9. Index map of the Philippines showing Manila (the Capital) and several major volcanoes including Taal. Courtesy of Lyn Topinka (US Geological Survey).

Figure 10. A map showing Taal caldera and surroundings. Notice that the caldera lies at the intersection of major faults and the topographic margin extends well beyond the caldera lake's margin. Courtesy of NASA Earth Observing System (EOS) Volcanology and their slide set compiled by Peter Mouginis-Mark (University of Hawaii).

Figure 11. Photo of the Taal caldera lake and Volcano Island taken from the N in November 1999. Courtesy of NASA Earth Observing System (EOS) Volcanology and their slide set compiled by Peter Mouginis-Mark (University of Hawaii).

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) announced in August 2008 that seismic unrest continued. On 28 August 2008, ten volcanic earthquakes occurred, two of which were felt and heard as rumbling sounds by residents in the Pira-Piraso village on Volcano Island. The earthquakes were located NE of the island near the Daang Kastila area (below Taal caldera's N rim) at estimated depths of 0.6-0.8 km. Surface observations indicated no change in the main crater lake area. The Alert Level remained at 1 (scale is 0-5, with 0 referring to No Alert).

On 8 June 2010, PHIVOLCS raised the Alert Level for Taal to 2 because of changes in several monitored parameters that began in late April. Since 26 April, the number and magnitude of volcanic earthquakes had increased. Most signals were high-frequency earthquakes, but at least one, on 2 June, was low-frequency. Steam emissions from the N and NE sides of Main Crater occasionally intensified. Deformation data showed slight inflation since 2004; measurements taken at the SE side of Taal on 7 June showed further inflation by 3 mm.

In addition to increased seismicity, the temperature of the Main Crater Lake increased from 32°C on 11 May to 34°C on 24 May. According to PHIVOLCS, the ratios of Mg:Cl and SO4:Cl, as well as total dissolved solids in the lake, all increased. Temperature measurements of the main crater lake did not increase further, remaining between 33-34°C.

PHIVOLCS proposed that the high frequency earthquakes could be the result of active rock fracturing associated with magma intrusion beneath the volcano, and that the fractures could serve as passageways through which hot gases from the intruding magma could escape into the lake.

According to news reports (Xinhua, Philippine Daily Inquirer), the more than 5,000 residents living near Taal were advised to evacuate their homes voluntarily. On 10 June, the Philippine Coast Guard sent five teams of divers and rescue swimmers with rubber boats and medical teams to its forward command post to help evacuate, if necessary, these residents. A news report (Philippine Daily Inquirer), however, indicated that most residents refused to leave without an official order.

The number of earthquakes recorded daily gradually declined to background levels beginning the second week of July 2010. Hydrothermal activity in the N and NE sides of the main crater and Daang Kastila also decreased. Precise leveling measurements conducted during 13-21 July along the NE, SE, and SW flanks detected minimal inflation. On 2 August, PHIVOLCS lowered the Alert Level to 1.

According to PHIVOLCS, seismic activity increased during the first week of September 2010. From 1-27 September 2010, a total of 274 volcanic earthquakes, or an average of 10 events/day, was recorded. However, given that field surveys conducted at the Main Crater and at the 1965-1977 "New Eruption" site (SW edge of Main Crater) indicated no anomalous thermal or surface activity.

PHIVOLCS reported that a December 2010 deformation survey showed slight inflation compared to a September 2010 survey. Field observations on 10 and 18 January revealed no significant changes. Weak steaming from a thermal area inside the main crater was noted and the lake temperature, acidity, and color were normal. During 15-16 January 2011, ten volcanic earthquakes were detected, two of which were felt by residents of Pira-Piraso, on the N side of the island. On 17 January three volcanic earthquakes were detected and on 18 January only one was reported. Between 18-30 January, up to seven daily volcanic earthquakes were detected by the seismic network.

Field observations during 23-25 January 2011 revealed an increase in the number of steaming vents inside the main crater and a drop in the lake level there. The lake water temperature and pH values remained normal. Visual observations on 27 January showed weak steaming at a thermal area in the crater.

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Synonyms

Pulo | Volcano Island | Bombon, Lake

Cones

Feature Name

Feature Type

Elevation

Latitude

Longitude

Balantok

Cone

Batulao, Mount

Stratovolcano

693 m

14° 3' 0" N

120° 48' 0" E

Binintiang Malaki
Binintiang Malaqui

Cone

263 m

Binintiang Munti

Cone

60 m

Macolod
Makulot

Stratovolcano

957 m

13° 55' 0" N

121° 3' 0" E

Makiling, Mount

Stratovolcano

1090 m

14° 8' 0" N

121° 12' 0" E

Piro-Piraso

Cone

Sungay, Mount

Stratovolcano

620 m

14° 8' 0" N

121° 2' 0" E

Tabaro, Mount

Vent

Craters

Feature Name

Feature Type

Elevation

Latitude

Longitude

Talisay

Caldera

Basic Data

Volcano Number

Last Known Eruption

Elevation

LatitudeLongitude

273070

1977 CE

311 m / 1020 ft

14.002°N
120.993°E

Volcano Types

Caldera Pyroclastic cone(s) Tuff ring(s)

Rock Types

MajorAndesite / Basaltic AndesiteBasalt / Picro-BasaltDacite

MinorRhyolite

Tectonic Setting

Subduction zoneContinental crust (> 25 km)

Population

Within 5 kmWithin 10 kmWithin 30 kmWithin 100 km

717,090
717,090
2,380,326
24,814,047

Geological Summary

Taal is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Though not topographically prominent, its prehistorical eruptions have greatly changed the topography of SW Luzon. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, and several eruptive centers lie submerged beneath the lake. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all historical eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones that has grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.

References

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography.

Deformation History

There is data available for 6 deformation periods. Expand each entry for additional details.

Deformation during 2005 Mar - 2005 Jul [Subsidence; Observed by GPS]

Start Date: 2005 Mar

Stop Date: 2005 Jul

Direction: Subsidence

Method: GPS

Magnitude: Unknown

Spatial Extent: Unknown

Latitude: Unknown

Longitude: Unknown

Time series of dual-frequency GPS stations (coordinates in mm with respect to KAYT) from June 1998 to July 2005. Alternating periods of inflation and deflation are reflected by the time series data, by plots that show East, North, and vertical coordinate component change for stations (A) TVST (1998?2005), (B) PINT (1998?2000)/TGYT (2001?2005), and (C) MMA8 (crosses, June to November 1998)/PIMO (1998 to 2005). Red circles and crosses represent positions, while vertical bars (cyan) depict are 95% errors scaled to repeatability. PIMO and MMA8 are dual-frequency stations situated in Manila, ~30 km north of the Caldera, while PINT was formerly the GPS station situated at the present location of TV07. Boxes indicate the deflationary (box with thin solid line) and inflationary periods (boxes with dashed lines) under study.

Deformation during 2004 Jun - 2005 Mar [Uplift; Observed by GPS]

Remarks: Deformation at Taal Volcano can be modeled by spherical Mogi source beneath Volcano Island''s central crater and is likely magmatic in origin

Time series of dual-frequency GPS stations (coordinates in mm with respect to KAYT) from June 1998 to July 2005. Alternating periods of inflation and deflation are reflected by the time series data, by plots that show East, North, and vertical coordinate component change for stations (A) TVST (1998?2005), (B) PINT (1998?2000)/TGYT (2001?2005), and (C) MMA8 (crosses, June to November 1998)/PIMO (1998 to 2005). Red circles and crosses represent positions, while vertical bars (cyan) depict are 95% errors scaled to repeatability. PIMO and MMA8 are dual-frequency stations situated in Manila, ~30 km north of the Caldera, while PINT was formerly the GPS station situated at the present location of TV07. Boxes indicate the deflationary (box with thin solid line) and inflationary periods (boxes with dashed lines) under study.

Deformation during 2000 Feb - 2000 Nov [Uplift; Observed by GPS]

Remarks: Deformation at Taal Volcano can be modeled by spherical Mogi source beneath Volcano Island''s central crater and is likely magmatic in origin

Time series of dual-frequency GPS stations (coordinates in mm with respect to KAYT) from June 1998 to July 2005. Alternating periods of inflation and deflation are reflected by the time series data, by plots that show East, North, and vertical coordinate component change for stations (A) TVST (1998?2005), (B) PINT (1998?2000)/TGYT (2001?2005), and (C) MMA8 (crosses, June to November 1998)/PIMO (1998 to 2005). Red circles and crosses represent positions, while vertical bars (cyan) depict are 95% errors scaled to repeatability. PIMO and MMA8 are dual-frequency stations situated in Manila, ~30 km north of the Caldera, while PINT was formerly the GPS station situated at the present location of TV07. Boxes indicate the deflationary (box with thin solid line) and inflationary periods (boxes with dashed lines) under study.

Deformation during 1999 Apr - 2000 Jan [Subsidence; Observed by GPS]

Remarks: Deformation at Taal Volcano can be modeled by spherical Mogi source beneath Volcano Island''s central crater and is likely magmatic in origin

Time series of dual-frequency GPS stations (coordinates in mm with respect to KAYT) from June 1998 to July 2005. Alternating periods of inflation and deflation are reflected by the time series data, by plots that show East, North, and vertical coordinate component change for stations (A) TVST (1998?2005), (B) PINT (1998?2000)/TGYT (2001?2005), and (C) MMA8 (crosses, June to November 1998)/PIMO (1998 to 2005). Red circles and crosses represent positions, while vertical bars (cyan) depict are 95% errors scaled to repeatability. PIMO and MMA8 are dual-frequency stations situated in Manila, ~30 km north of the Caldera, while PINT was formerly the GPS station situated at the present location of TV07. Boxes indicate the deflationary (box with thin solid line) and inflationary periods (boxes with dashed lines) under study.

Deformation during 1999 Jan - 1999 Mar [Uplift; Observed by GPS]

Remarks: Deformation at Taal Volcano can be modeled by spherical Mogi source beneath Volcano Island''s central crater and is likely magmatic in origin

Time series of dual-frequency GPS stations (coordinates in mm with respect to KAYT) from June 1998 to July 2005. Alternating periods of inflation and deflation are reflected by the time series data, by plots that show East, North, and vertical coordinate component change for stations (A) TVST (1998?2005), (B) PINT (1998?2000)/TGYT (2001?2005), and (C) MMA8 (crosses, June to November 1998)/PIMO (1998 to 2005). Red circles and crosses represent positions, while vertical bars (cyan) depict are 95% errors scaled to repeatability. PIMO and MMA8 are dual-frequency stations situated in Manila, ~30 km north of the Caldera, while PINT was formerly the GPS station situated at the present location of TV07. Boxes indicate the deflationary (box with thin solid line) and inflationary periods (boxes with dashed lines) under study.

Deformation during 1998 Jun - 1998 Dec [Subsidence; Observed by GPS]

Remarks: Deformation at Taal Volcano can be modeled by spherical Mogi source beneath Volcano Island''s central crater and is likely magmatic in origin

Time series of dual-frequency GPS stations (coordinates in mm with respect to KAYT) from June 1998 to July 2005. Alternating periods of inflation and deflation are reflected by the time series data, by plots that show East, North, and vertical coordinate component change for stations (A) TVST (1998?2005), (B) PINT (1998?2000)/TGYT (2001?2005), and (C) MMA8 (crosses, June to November 1998)/PIMO (1998 to 2005). Red circles and crosses represent positions, while vertical bars (cyan) depict are 95% errors scaled to repeatability. PIMO and MMA8 are dual-frequency stations situated in Manila, ~30 km north of the Caldera, while PINT was formerly the GPS station situated at the present location of TV07. Boxes indicate the deflationary (box with thin solid line) and inflationary periods (boxes with dashed lines) under study.

Emission History

There is no Emissions History data available for Taal.

Photo Gallery

Binintiang Malaki, a pyroclastic cone at the NW tip of Volcano Island, was formed during an eruption in 1707. The 263-m-high cone, seen here from the SW, is the largest of the flank cones on Volcano Island, to which it is connected by a broad isthmus.

Photo by Kurt Frederickson, 1968 (Smithsonian Institution).

An eruption that began on January 31, 1968, produced a cinder cone, whose steaming crater is seen at the lower right. The dark lava flow that extends from the cinder cone to produce a lava delta in Lake Taal was emplaced during the 1968 eruption, which lasted until April 2. This December 1968 aerial view from the NE shows the black 1968 cinder cone, which was constructed within a 1966 tuff cone whose rim is at the lower right. The lava flow traveled to the lake within an elongated crater produced during the major 1965 eruption.

Photo by Kurt Frederickson, 1968 (Smithsonian Institution).

An eruption column rises above a vent on the SW side of Volcano Island on September 30, 1965. The white cloud at the base is a horizontally moving base surge. The white scale bar at the upper right is about 500-m long. Devastating pyroclastic surges were produced during the two-day eruption, which began on September 28 and caused 150 fatalties.

A small, 3-km-wide caldera is located at the center of Volcano Island, in the Philippines' southern Luzon Island. The 5-km-wide Volcano Island lies within a much larger, 15 x 20 km Taal caldera, whose low, western wall is seen across Lake Taal in the distance. The small island in the center of the photo, a remnant of historical eruptions on Volcano Island, is a geographical oddity--an island in a lake on an island in a lake on an island.

Photo by Chris Newhall, 1989 (U.S. Geological Survey).

Taal caldera, seen here from its NW rim, is a 15 x 20 km caldera of Pleistocene and Holocene age. Volcano Island, in the north-central part of Lake Taal, has been the site of all historical eruptions at Taal volcano. The island is constructed of coalescing small stratovolcanoes, tuff rings, and scoria cones. Powerful phreatomagmatic explosive eruptions have occurred from several locations on the 5-km-wide Volcano Island and have produced pyroclastic surges that have made Taal the most deadly volcano of the Philippines.

Photo by Chris Newhall, 1978 (U.S. Geological Survey).

The small, steaming tuff ring in the center of the photo was produced towards the end of a powerful 1965 explosive eruption of Taal volcano in the Philippines. The brief, 2-day eruption from September 28 to 30, which originated from a fissure on the SE flank of Volcano Island, produced devastating pyroclastic surges when lake water gained access to the vent. The elongated vent is filled by an inlet of Lake Taal in this 1965 post-eruption photo from the south. Eruptions the following year almost completely filled this new inlet.

Photo by Jim Moore, 1965 (U.S. Geological Survey).

This 400-m-wide crater was formed during an eruption in 1976. The NE-SW-trending explosion crater greatly modified a series of cones and craters that had been constructed during yearly eruptions from 1966 to 1970 within a large elongated crater which was formed during the 1965 eruption. This 1984 photo from the SW also shows a very small crater that was created in 1977 crater along the wall at the margin of the flat bench at the upper right side of the 1976 crater.

Photo by Chris Newhall, 1989 (U.S. Geological Survey).

This view of Main Crater Lake, filling a small 3-km-wide caldera on Volcano Island, looks across distant Lake Taal to the NE rim of the 15 x 20 km Taal caldera. The surface of 267 sq km Lake Taal is only 3 m above sea level. Volcano Island has been the source of all historical eruptions of Taal volcano. Powerful explosive eruptions have produced pyroclastic surges that swept across Lake Taal and devastated lake shore areas. Powerful Pleistocene eruptions that formed Taal caldera greatly modified the topography of southern Luzon Island.

Photo by Chris Newhall, 1989 (U.S. Geological Survey).

Mount Tabaro, seen here from the west in 1992, is the highest point on Volcano Island. The diagonal ridge extending across the photo from the lower right shoreline is the rim of the elongated 1965 vent system. The dark lava flow at the coastline was erupted in 1968 from a cinder cone at the head of the 1965 vent. This and other overlapping cinder cones and craters at the right center were formed during eruptions from 1966 to 1977.

Photo by Chris Newhall (U.S. Geological Survey).

GVP Map Holdings

The maps shown below have been scanned from the GVP map archives and include the volcano on this page. Clicking on the small images will load the full 300 dpi map. Very small-scale maps (such as world maps) are not included. The maps database originated over 30 years ago, but was only recently updated and connected to our main database. We welcome users to tell us if they see incorrect information or other problems with the maps; please use the Contact GVP link at the bottom of the page to send us email.

Affiliated Sites

The DECADE portal, still in the developmental stage, serves as an example of the proposed interoperability between The Smithsonian Institution's Global Volcanism Program, the MAGA Database, and the EarthChem Geochemical Portal. The Deep Earth Carbon Degassing (DECADE) initiative seeks to use new and established technologies to determine accurate global fluxes of volcanic CO2 to the atmosphere, but installing CO2 monitoring networks on 20 of the world's 150 most actively degassing volcanoes. The group uses related laboratory-based studies (direct gas sampling and analysis, melt inclusions) to provide new data for direct degassing of deep earth carbon to the atmosphere.

WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.

Middle InfraRed Observation of Volcanic Activity (MIROVA) is a near real time volcanic hot-spot detection system based on the analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) data. In particular, MIROVA uses the Middle InfraRed Radiation (MIR), measured over target volcanoes, in order to detect, locate and measure the heat radiation sourced from volcanic activity.

Using infrared satellite Moderate Resolution Imaging Spectroradiometer (MODIS) data, scientists at the Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, developed an automated system called MODVOLC to map thermal hot-spots in near real time. For each MODIS image, the algorithm automatically scans each 1 km pixel within it to check for high-temperature hot-spots. When one is found the date, time, location, and intensity are recorded. MODIS looks at every square km of the Earth every 48 hours, once during the day and once during the night, and the presence of two MODIS sensors in space allows at least four hot-spot observations every two days. Each day updated global maps are compiled to display the locations of all hot spots detected in the previous 24 hours. There is a drop-down list with volcano names which allow users to 'zoom-in' and examine the distribution of hot-spots at a variety of spatial scales.

EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).